CBSESolved Test Papers

PHYSICSClass XII

Chapter : Electronic Devices

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CBSE TEST PAPER-01

CLASS - XII PHYSICS (Solid and Semiconductor Devices)

1. Give the ratio of number of holes and the no. of conduction electrons in an intrinsic

semiconductor. [1]

2. What type of impurity is added to obtain n-type semiconductor? [1]

3. Doping of silicon with indium leads to which type of semiconductor? [1]

4. Draw a pn junction with reverse bias? Which biasing will make the resistance of a

p-n-junction high? [2]

5. Write the truth table for the following combination of gates? [2]

6. Draw the voltage current characteristics of a zener diode? [2]

7. What is an ideal diode? Draw the output wave form across the load resistor R, if the

input waveform is as shown in the figure. [2]

8. With the help of a labeled circuit diagram, explain full wave rectification using junction

diode. Draw input and output wave forms? [3]

9. Distinguish between conductors, insulators and semiconductors on the basis of energy

band diagrams? [3]

10. The following truth table gives the output of a 2-input logic gate.

A B output

0 0 1

0 1 0

1 0 0

1 1 0

Identify the logic gate used and draw its logic symbol. If the output of this gate is fed

as input to a NOT gate, name the new logic gate so formed? [3]

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CBSE TEST PAPER-01

CLASS - XII PHYSICS (Solid and Semiconductor Devices)

[ANSWERS]

Ans1: 1nh

ne (As in intrinsic semiconductor ne = nh)

Ans2: Pentavalent atoms like Arsenic (As)

Ans3: Indium is a trivalent impurity, thus doping of silicon with indium leads to p-type

semiconductor.

Ans4:

Reverse biasing will make the resistance high as it will not allow the current to pass.

Ans5:

A B Y’ Y

0

0

1

1

0

1

0

1

0

1

1

1

0

0

1

1

Ans6:

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Ans7: An ideal diode has zero resistance when forward biased and an infinite resistance when it is

reverse biased. Output wave from is

Ans8: Full wave rectifier consists of two diodes and a transformer with central tap. For any half

cycle of a.c. input only one diode is forward biased where as the other one is reverse biased.

Suppose for positive half of a.c. input diode D1 is forward biased and D2 is reverse biased,

then the current will flow across D1 where as for negative half of a.c. input diode D2 is

forward biased and the current flows across D2. Thus for both the halves output is obtained

and current flows in the same direction across load resistance R2 and thus a.c. is converted

into d.c.

Ans9: Conductor – Conduction band in a conductor is either partially filled or conduction and

valence band overlaps each other. There is no energy gap in a conductor.

Insulators – conduction band and valence band of all insulator are widely separated by and

energy gap of the order 6 to 9eV

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Also conduction band of an insulator is almost empty.

Semiconductor – In semiconductors the energy gap is very small i.e. about 1ev only.

Ans10: The gate is NOR gate.

If the output of NOR gate is connected to a NOT gate then the figure will be

New truth table is

A B Y

0 0 0

0 1 1

1 0 1

1 1 1

It is the truth table of OR gate

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